In recent years, research and development efforts have been intense on developing combinations of light sources and phosphors that will yield useful, high-performing light emitting devices, with the result that both efficient high-power light sources and efficient phosphors have been demonstrated. For example, both light emitting diode (“LED”) chips and phosphors for phosphor-converted LED (“pcLED”) devices have been demonstrated. A unique aspect of some phosphor/light source combinations (such as pcLEDs) is that the phosphors are in contact with the light source (such as a LED chip), and the light sources operate at high temperatures. For example, typical junction temperatures of high power LEDs are in the range of 80° C.-150° C. At these temperatures, the crystal of the phosphor is at a high vibrationally excited state, causing the LED excitation energy to be directed to heat emission through lattice relaxation rather than to the desired luminescence emission. Moreover, these lattice relaxations produce further heating, thereby further reducing the luminescence emission. This is a vicious cycle that precludes successful applications of existing phosphor materials. The pcLED lamp for general illumination application requires high optical energy flux (e.g., higher than 1 Watt/mm2) which causes additional heating by a Stokes shift generated inside the phosphor crystals. Successful development of light emitting devices incorporating both phosphors and a light source, such as pcLED lamps for general illumination, therefore requires the development of phosphors that can operate highly efficiently at temperatures of 80° C.-150° C. The risk is that it is difficult both to achieve 90% quantum yield at room temperature and to have high thermal stability at 80° C.-150° C. The thermal stability of a phosphor's luminescence is an intrinsic property of the phosphor which is determined by both the composition and the structure of the crystalline material.
Carbonitride and carbidonitride phosphors have recently been identified as promising candidates for overcoming the above challenges, yielding phosphors have excellent thermal stability and high emission efficiency. However, when combining phosphors with laser diodes to produce white light, a further challenge presents itself: achieving white light of satisfactory hue and color rendering properties. Previously, yellow-emitting phosphors have been used to create white light LED devices, but these devices have not produced desirable, warm white light.